1. Field of the Invention
The present invention relates to piping having a joining portion and used, for example, for a portion of a refrigeration cycle of an air-conditioning system for vehicle use. More particularly, the present invention relates to a method of manufacturing piping by means of plastic working. The present invention also relates to a method of adjusting the length of piping which is automatically conducted in the method of manufacturing it.
2. Explanation of the Related Art
Concerning the refrigerant pipes to connect various components with each other in a refrigeration cycle of an air-conditioning system used for a vehicle and concerning, for example, the refrigerant pipes, one is an outlet pipe and the other is an inlet pipe, to connect a refrigerant compressor, a condenser and a receiver, which are provided in an engine compartment, with an evaporator provided in a passenger compartment. The two refrigerant pipes are arranged together in parallel with each other in the front and at the rear of an expansion valve which is arranged so that the end portions of the two refrigerant pipes can be inserted into the expansion valve. In this case, it is unnecessary for a low pressure pipe, which guides a refrigerant from the evaporator to the compressor, so that the refrigerant can be returned, without passing through the expansion valve. However, in order to handle the two pipes easily, one being an outlet pipe and the other being a returning, both end portions of the two pipes located in the front and at the rear of the expansion valve are brazed to the same connector. In this way, the two pipes and the two connectors are connected and integrated with each other into one body by joining portions. Pipes having the joining portions, which are formed by being integrated with the pipes, are used in many cases.
In the case where these pipes are manufactured, even when one end portion of each of the two pipes is brazed to the connector, unless the other end portion of each of the two pipes is accurately machined so that it can be fitted at a predetermined position, it is impossible to positively connect both end portions of the two pipes with the two connectors. However, it is common that the refrigerant pipes provided in the refrigeration cycle of the air-conditioning system for vehicle use are bent into a complicated profile. Therefore, it is very difficult for the other end portions of the two bent pipes, which have already been cut and bent, to be accurately adjusted to the respective predetermined positions in the other connectors. Accordingly, before the pipes are brazed to the connector, it is necessary to previously repair the individual pipes so as to adjust the bending state and the profiles of the end portions of the pipes, that is, it is necessary to enhance the accuracy of the individual pipes which are used as parts of the air-conditioning system. Of course, this repair work causes an increase in the manufacturing cost of the pipe having the joining portion.
The above problems are not limited to the pipes having the joining portions used for the refrigerating cycle into which the two pipes and two connectors are incorporated. The above problems are caused even in the case of manufacturing a bent pipe, both end portions of which are brazed to two connectors, which must be respectively attached at a predetermined position in a predetermined posture. In the case where both end portions of a large number of bent pipes, the number of which is not less than three, are brazed to the same connector so as to manufacture a single pipe, the end portions of all pipes must be aligned in the same connector. Therefore, it is necessary to enhance the accuracy of the pipes, which are parts, which increases the manufacturing cost of the pipe having the joining portion. When the pipe and the connector are joined to each other by means of brazing, the joining strength can be positively enhanced. On the other hand, it is necessary to check for leakage of a fluid, which increases the manufacturing cost.
In this connection, although the detailed explanations will be made later, in a portion of the embodiment of the present invention, there is provided a pipe in which buckling is caused as a method for reducing the length of the pipe. The first prior art, which is approximately similar to this method, is disclosed in Japanese Unexamined Patent Publication No. 2000-343170 as a method of forging a pipe. According to the first prior art, when a force is given to an end face of a pipe, an excess metal in the middle portion of the pipe in the longitudinal direction is pushed to a relief space formed in a metallic die to support a cylindrical side of the pipe, so that the length of the pipe can be reduced by a quantity of the excess metal pushed to the side.
However, the first prior art is a technique capable of being applied to a straight pipe, the length of which is several times as long as the diameter of the pipe. Therefore, it is impossible to apply this technique to a refrigerant pipe, which is a main object of the present invention, the length of which is long and the profile of which has a plurality of bent portions.
As the second prior art, the Japanese Examined Patent Publication No. 3281997 discloses a connector used for connecting pipes, the appearance of which is partially similar to the pipe having a joining portion of the present invention. However, according to the second prior art, it is an object to form a fluid passage in a solid block used for connection, the profile of which is predetermined, and a pipe is inserted into a hole of this solid block used for connection. When the block for connection is held between a seat portion of a large diameter, which is previously formed in the pipe, and an expanded diameter portion which is formed in an end of the pipe, the pipe is integrated with the inside of the block.
According to the second prior art, the length of the pipe between the large diameter seat portion and the expanded diameter portion is always the same as the length of the hole of the block for connection, that is, there is no possibility that the length of the pipe between the large diameter seat portion and the expanded diameter portion is different from the length of the hole of the block for connection. Therefore, the second prior art includes no intention that the length of a pipe, the length of which inevitably fluctuates because a bent portion is formed in the pipe, is adjusted to an arbitrary value. Accordingly, although the appearance of the second prior art is partially similar to that of the present invention, the second prior art is essentially different from the art of the present invention. Therefore, it is impossible for the second prior art to adjust the length of the pipe to an arbitrary value when an extended diameter portion is machined at the end portion of the pipe.